Ingroup favoritism in cooperation: A meta-analysis.

Although theory suggests individuals are more willing to incur a personal cost to benefit ingroup members, compared to outgroup members, there is inconsistent evidence in support of this perspective. Applying meta-analytic techniques, we harness a relatively recent explosion of research on intergroup discrimination in cooperative decision making to address several fundamental unresolved issues. First, summarizing evidence across studies, we find a small to medium effect size indicating that people are more cooperative with ingroup, compared to outgroup, members (d = 0.32). Second, we forward and test predictions about the conditions that moderate ingroup favoritism from 2 influential perspectives: a social…